# Preheat oven to 160C.
# Grease a 28x18cm baking tin and line bottom with baking paper, overlap paper at opposite long ends for ease of removal.
# Beat the butter and sugar in a small bowl until creamy.
# Add the eggs one at a time, beating well after each addition.
# Mix the vanilla and coffee in 1 tablespoon warm water, stir until dissolved.
# Add coffee to butter mixture and beat until combined.
# Pour mixture into a large bowl.
# With a large spoon, fold in the sifted flours alternately with the sour cream. Stir until just combined.
# Spoon the mixture into the prepared tin and smooth the surface.
# Bake for 30-40 minutes or until a skewer comes out clean when inserted in the centre.
# Set aside for 5 minutes, then turn onto a wire rack to cool.